Submarine Geomorphology and Evolution of the Dokdo and Ulleung Volcanic Edifices in the East Sea

Dokdo and Ulleungdo are volcanic edifices developed in the East Sea and show a clear contrast in their formation ages and evolutionary processes. The Dokdo volcano is an eroded volcanic edifice characterized by a flat summit at a water depth of approximately 200 m, forming a guyot-type morphology with small islets. The summit area reaches ~84.6 km² and is larger than the subaerial area of Ulleungdo. Approximately six levels of submarine terraces are developed on the summit, reflecting repeated Quaternary sea-level fluctuations. Bedrock exposure is dominant in the northern summit, whereas the southern part is sediment-rich, and an east–west alignment of small craters suggests the directional control of late-stage volcanic activity. The Dokdo volcano can be subdivided into a flat summit, a steep flank, and a gently sloping base. The flanks are characterized by submarine canyons and ridges with various orientations. Slope analysis indicates very steep gradients of up to ~27–30° along the canyons, implying repeated sediment transport and mass-movement processes. In the northern basal area, small cone-shaped positive reliefs are observed, and backscatter data indicate a mixture of exposed bedrock and sediment-covered surfaces. In contrast, Ulleungdo represents a relatively young, single-cone submarine volcano with a central volcanic island and steep flanks descending to depths of ~2,200 m. Radial lava ridges and lava fields are developed down to ~200 m water depth, while submarine canyons and debris lobes formed by repeated slope failures are concentrated between 600 and 1,200 m. The volcanic base consists of deep-sea sediment fans formed by gravity flows and turbidity currents, and only two levels of submarine terraces are developed on the continental shelf, in clear contrast to the multi-level terraces of Dokdo. Between Dokdo and Ulleungdo, the Anyongbok Seamount, with a summit depth of ~473 m, shows a pointed conical morphology without a wave-cut platform and a dominant north–south ridge. The concave summit geometry suggests the presence of a collapsed crater. Based on radiometric ages and geomorphic characteristics, the submarine volcanic edifices in the East Sea are inferred to have formed sequentially from Dokdo to Anyongbok Seamount and finally to Ulleungdo. These contrasting geomorphic features provide important constraints on the timing, eruptive styles, and spatiotemporal evolution of submarine volcanism in the East Sea.